This invention is in the field of infrared birefringent materials, and structures which may be made to exhibit birefringent properties. By definition, a birefringent material is one that exhibits optical properties which depend upon the polarization of an input radiation field. This usually means that the optical index of refraction, as seen by an electro-magnetic wave propagating through the material, depends upon the orientation of the electric field vector. Unfortunately, the number of materials which exhibits a high degree of such birefringent is limited, particularly in the 8-13 micron wavelength region of the electromagnetic sprectrum, where optically active transparent materials are rare. Birefringent materials can be used to fabricate wide field-of-view, narrow bandwidth filters. They can be used to rotate the polarization of an input field or to convert circular polarization to plane polarization and vice versa. In each of these cases, the material must produce a low insertion loss, i.e., transmit the input wavelength with low absorption, while at the same time exhibiting a large optical asymmetry. There are few naturally occuring materials which possess all of these properties. Some of the best candidates are listed below along with their shortcomings. In the visible region, lithium niobate and lithinum tantalate are transparent; but, since their birefringence is not large, a large optical path length is required to produce a usable effect. Tungsten bronze type crystals, such as strontium barium niobate, can be used from the visible region out to seven microns, can be grown in large optical quality crystals, but suffer limited birefringence. Chalcopyrite type crystals, which transmit in the 8-13 micron region, possess limited birefringence and are not available in large optical quality sizes. Finally, sapphire is the best choice for the millimeter wave to infrared region, barring the areas where vibrational resonances occur. Like those listed previously, it also suffers from a small optical asymmetry.
In view of the severe lack of available materials, it is clearly desirable to develop techniques which would allow the fabrication of a medium which possesses artifically generated birefringent properties. We have invented such materials and call them birefringent artificial dielectrics.